The present invention relates to electronic fuel injection for internal combustion engines.
In electronic fuel injection various engine operating parameters are sensed to give information on engine input and output conditions to an electronic control unit where the sensed variables are processed to optimize the fuel quantity delivered to each cylinder. To decelerate an engine, fuel is conventionally cut off by sensing the throttle being nearly closed while the engine speed is above a predetermined level. Although this fuel cut-off feature is advantageous in terms of exhaust emissions and driveability during deceleration, it is disadvantageous when the driver attempts to accelerate the engine by changing transmission gear ratios while operating the clutch to momentarily disengage the engine from transmission, since during these operations throttle is nearly closed to cut off fuel briefly so that mixture is leaned while the engine requires enrichment. This introduces a rapid change in air fuel ratio resulting in the production of a substantial amount of noxious emissions and a momentary loss of engine power. Particularly, for a closed-loop fuel control system using a feedback signal derived from an exhaust gas sensor, the introduction of such a rapid change in air-fuel ratio will cause the system to oscillate abnormally. This problem may find its solution in the use of a conventional dashpot type throttle in which the movement of the throttle as it approaches the nearly closed position is damped. However, the damping operation results in poor driveability due to partial loss of engine brake and an increase in cost for additional mechanical components.